VOX AC15C1 Schematics

[Bug2222]

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[brunomariano]

I got them all at banzaieffects.com. Only miss the Kiwame resistors.

I've already changed the plate resistors to 220k and bypassed R1. Don't noticed any out of normal clipping on low volumes. Now it sounds fuller with a lot more bass.

I've ordered a choke from a Brazilian maker, very well recomended, but the chokes he make are only 8H. Do you know what difference I will hear?

Thanks!

[brunomariano]

Almost forgot: I can't find 140R @ 5W kiwame (or any other brand) resistors, just 130R or 150R. Is that right?

[Bug2222]

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[brunomariano]

Thank you for all your answers, Bug2222!

In you case, as you disposed the choke on your schematic, you are using it just to filter B1, right?

And what do you think about doing the opamp bypass switchable? I'm thinking of doing that with a push pull pot on the reverb control.

Thanks!

[Bug2222]

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[brunomariano]

I think it will not work with a push/pull potentiometer switchable. There are too many parameters involved (R22,R23,C19 and "R1") How do you select them all with only a push/pull pot to correct the signal strength adjustment? When you use the amp anyway more for clean sounds it's not a good idea to use the R1 Jumper with the opamps.

I don't need to correct the signal strenght because I will not switch the opamps and reverb on and off on a live situation.

[Bug2222]

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[brunomariano]

Sorry, don't mean to be rude.

I just misunderstand what you have posted before, when you say that make it switchable "dont work". It'll work, I mean, the push pull will put the opamp/reverb on the signal chain and bypasses it as well, but there will be a signal loss when I switch the reverb on. For my commom use of this amp, it is acceptable. Probably most of the live situation I'll use the reverb bypassed. But sometimes at home practice, at low levels, It's nice to just plug the guitar straigh in the input and add some reverb.

[brunomariano]

Hi!

Do you guys saw that schematic, from a previous version of AC15?

http://www.tdpri.com/forum/amp-central- ... -here.html" onclick="window.open(this.href);return false;

Look at the point they are taking the signal to feed the reverb. Also, there is no OPAMPS on the signal chain beside the ones dealing with the reverb.

Also, checking some fender schematics, they take the reverb after the eq, sometimes after the last gain stage, and don't use opamps to mix signal. I think the same can be done to AC15C1.

[Bug2222]

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[brunomariano]

I just don't understand why, in the AC15CC1, they take the singal to feed the reverb for that point inside the EQ circuit.

[Moose]

VOX AC15C1 MODS TIPS. First I would like to thank inkmodo.dragon for schematic effort! That's how I discovered this site. I repair and mod tube amps in my area and would like to share what I have found on the AC15C1 that others might find helpful.
1) The Choke Mod--Not really worth it... I bought the Mercury Magnetics 10 henry choke, 100mA, ohmed out at 270. It's a fine iron but there are others that will do just as well for much less, Classic Tone for example. I mounted the choke in the available spot under the ac power in. Removed the board , you dont have to remove any wire connections, and unsolder R80. There is a little indent in the plywood back cover-facing the back of the amp to the right of the ac plug, that can widened a bit and here I installed a quality DPDT slide switch. On one end I soldered the choke the other I soldered R80. The center lugs go to the board. Now I can switch between the stock R80 and the choke( note: I turn the amp off before switching so not to risk a spike in the IC parts). FINDINGS: There is a 20V increase on the plates with the choke. Stock was 325V with R80, 345V with the choke. I 'm using '80s NOS Reflector 7189s that dont mind the higher voltage. There was really no change in tone. There is a very slight difference in headroom due to the higher voltage. The amp was and still is dead quiet with both. I found myself going back to the R80 in the small room I was playing in. I will probably only use the choke on stage playing loud. Knowing what I know now I would not buy the choke. But I do like the choice to use with other tubes.
2) Bright Cap Mods-- It is not nessesary to unsolder the bright caps. Use wire cutters and cut down between the legs and crush the cap and clean off the ceramic. This leaves 2 nice legs to resolder to if you want. On the Top Boost side I dont like the bright cap, and removed C8 and C67 , did the standard bass pot mod soldering a wire from lug 3 to ground(the leg of what was C8). Greatly improved treble and bass response. Done. On the Normal side crush R4. While the board is out for the choke mod, Unsolder the bass pot,and solder in 3 three inch or so wires. The same for the 2 cap legs. Get an Alpha 500KA pot with a DPDT pull switch. Install with the terminals up and solder the wires to their respective lugs. Solder the bright cap wires to the switch lugs closest to the panel and the cap of your choice to the center 2 lugs. I used an 82pF silver mica. Take the time to this so not to deface the panel with a toggle switch.
3) Change to the MOD 8EB2C1B reverb tank
4) It goes without saying to ditch the Chinese tubes. Find the ones that suit your style and that's all this amp needs. I like this amp with no pedals, maybe a chorus on Normal. Just an AB foot switch between channels and done. Save your pedals for your other amps. Just my opinion. Cheers

[anix]

Hi guys.

First of all - inkomodo.dragon, thank you for your job!

Does anyone have measured the +VCC voltage?

[brunomariano]

Hey, why everything Bug2222 posted vanished?